1. Field of the Invention
Methods and devices consistent with the present invention relate to displaying, and more particularly, to a diffuser and a display device with an adjustable viewing angle employing the diffuser.
2. Description of the Related Art
With the recent development of communication technology and display device technology, many portable terminals, such as a personal digital assistant (PDA), a portable multimedia player (PMP), and a digital multimedia broadcasting (DMB) system, have been developed.
Liquid crystal displays (LCDs), which are non-emissive flat panel display devices often used in portable terminals, form an image by changing the fraction of light transmitted through a liquid crystal cell according to an applied voltage. Since LCDs cannot emit light by themselves, a separate light source device, such as a backlight unit, is required.
Such LCDs have a problem in that a viewing angle is narrow due to a difference between an optical path in which light emitted from the backlight unit vertically passes through the liquid crystal cell and an optical path in which light emitted from the backlight unit obliquely passes through the liquid crystal cell. To solve the problem, various attempts have been made to increase a viewing angle.
Meantime, although a wide viewing angle is often preferred, a narrow viewing angle is preferred in applications for privacy protection and security measures.
Accordingly, there have been attempted to develop display devices which can provide a narrow viewing angle in a private mode where privacy protection is necessary and a wide viewing angle in a public mode where a plurality of people need to share images.
A display device, which is disclosed in Japanese Patent Publication No. 1997-197405, includes a polymer dispersed liquid crystal (PDLC) layer disposed on a top surface of a liquid crystal panel. The PDLC layer shifts between a diffusing state and a transparent state according to an applied voltage. In the diffusing state, incident light is diffused, thereby providing a wide viewing angle, and in the transparent state, collimated light is transmitted without being diffused, thereby providing a narrow viewing angle.
However, since the display device disclosed in Japanese Patent Publication No. 1997-197405 requires the PDLC layer in order to adjust a viewing angle, manufacturing costs are increased. Also, since the thickness of a liquid crystal cell should be increased in order to improve the contrast of the PDLC layer, a voltage used to drive the PDLC layer is increased, and an optical path in which light input through the liquid crystal panel is transmitted through the PDLC is lengthened, thereby increasing the risk of image blurring.